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Sunday, 14 August 2011

T.V - 2mins To Know How It Works

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I can pretty confidently say that you would have watched a television today,and the reason i am sure is due to how extremely common T.Vs are nowadays. But how many of us actually know how the T.V we look at works and shows us the picture and sound ? So lets take a quick look at it.

At the very base, a T.V exploits two features of our brain, it :-

  • puts small nearby dots together to form an image
  • puts many still images together into a single image [click 'read more' to understand in detail with an example]
The dots (a.k.a pixels) are used to make all the pictures you see in cameras, computers,T.V, etc.When the dots are small enough and placed close enough, you can't differentiate the individual dots. 

So now that we've got that clarified, lets go to the T.V. A T.V is almost like a projector and screen put together. There is a little flashlight kinda thing ,a.k.a cathode ray tube (c.r.t), behind the screen. The T.V screen has a substance (phosphor) coated in the inner face that glows when the beam of light from the flashlight strikes it.

Now moving over to how it all works together. The CRT emits electron beams (think of it as a really thin beam of light) when voltage is applied to it. So by controlling the amount of voltage you can change the intensity of the beam. Your T.V screen has thousands of dots on the screen and when the beam from the CRT hits the dots they glow for a short time. 

The CRT has some coils on it which controls the movement of the tube, and hence helps it to point all over the screen.When you switch on the T.V, the controller tells the coil (and the CRT) where to move to and which dots on the screen  it should make glow. The CRT then moves across the screen more than 15,000 times a second and keeps making the required dots to glow in the correct intensity. Thus you get your picture on the screen, and the fast change of the successive images makes it seem like the characters are moving.

The information about which dots to make glow, for how long,intensity,etc. is what is sent to your T.V'c controller from your cable operator, VCR/DVD player, etc. 

And the sound signals are also sent to the T.V almost in the same way, but we'll explain about that in a later post, 'stay tuned' :-)
Some Extra Info

The black-and-white T.V (which are mostly obsolete now) screens just have one type of dots which have to glow or not to be white or black,respectively. In color T.V sets, each dot is actually made of 3 smaller dots of red,green and blue, which when mixed in different proportions gives you any color you want.

Try-it-yourself examples for the brain tricking concept

To see the dot principle in action,you can try it yourself by simply making a picture by starting to put dots placed nearby,but without touching each other, with a pencil.Keep going till you make a simple picture. Now step back 20 feet and look at the same picture and also look at it from 20inches from your face. You will notice how the dots seem to overlap when you look at it from a distance. In a T.V they just make the dots really small  in the first place so that you don't have to move away and see the action.

To see an example of the second feature shown by the brain, try holding a small l.e.d torch, face it towards you and move it really fast in a circular motion in front of you. You will realize that you can actually see a circular image of light,though there is no such image. That image is caused because your brain is not able to process the moving l.e.d fast enough, and stores each spot it sees the l.e.d but by then the l.e.d has moved forward, and thus it forms a continuous image. I'm guessing that the concept would be pretty clear then,plus its fun. :-)

This is the same principle which is used in Theaters, where they just rapidly move a reel of still images. But, we'll cover that in detail in another post. :-)
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